1. Field of the Invention
The present invention relates to a Zr compound which is suitable as a material for the formation of a Zr-containing metal oxide film useful as a ferroelectric film, optical thin film, catalytic thin film, solid electrolyte thin film, etc. by a chemical vapor deposition method (CVD method), to a process for manufacturing the same and to a liquid composition for the formation of a PZT film.
2. Description of the Prior Art
Considerations have been carried out for the formation of a PZT film which is a ferroelectric substance for nonvolatile memory by a CVD method. It has been also desired that the temperature for the formation of the film is as low as possible. Method for supplying the material in the CVD method is roughly classified into two. One is a method A where the pure material compound is introduced into a CVD chamber as it is or after carried with an inert carrier gas and another is a method B where the material compound is dissolved in an organic solvent and the solution is flash-evaporated and introduced into the CVD chamber. In any of those methods, there is a possibility that, before the mixed gas arrives the substrate, the components thereof react each other to lower the volatility or that a ligand exchange occurs to change the property. It is desirable that such a thing is avoided and also that decomposition characteristics of the compounds of Pb, Ti and Zr such as thermal decomposition temperature are similar. In the method B, the three components, i.e. Pb, Zr and Ti, are made into a single solution as an ultimate method but, in that case, it is requested that neither reaction nor deterioration takes place in the solution until being subjected to a CVD process.
With regard to a Pb material for the manufacture of a PZT film by the CVD method, that of a PbEt4 type and a Pb(dpm)2 type are available but, since the PbEt4 type is highly toxic, the Pb(dpm)2 type having weak toxicity is appropriate for a large-scale production. There has been a demand for Zr compound and Ti compound which are not reactive with Pb(dpm)2 and have similar thermal decomposition characteristics thereto. In the method B, an interaction with a solvent and a solubility are important factors as well.
With regard to the method A, Tatsumi, et al. disclosed in Extended Abstracts (59th Autumn Meet. 1998); Japan Society of Applied Physics, page 447 that crystallization at the temperature of as low as 430xc2x0 C. occurred by an extremely low-pressure CVD by supplying pure Pb(dpm)2-Zr(OtBu)4-Ti(OiPr)4 at its own pressure.
With regard to the method B, there is a disclosure in Japanese Patent Laid-Open No. 298762/1998 that film is formed by a CVD method from a combination of Pb dipivaloylmethanate-Zr dipivaloylmethanate-Ti dipivaloylmethanate (Pb:Zr:Ti=2.2:1:1) using THF as a solvent. Although no chemical formula is given for the Zr dipivaloylmethanate, it is presumed to be Zr(dpm)4 which was available at that time.
In claim 15, U.S. Pat. No. 5,820,664 (October 1998) discloses a solution of Pb(dpm)2-Zr(dpm)4-Ti(OiPr)2(dpm)2 in a mixed solvent of 45% to 88% of THF, 10% to 35% of isopropanol and 2% to 20% of tetraglyme.
P. C. Van Buskirk, et al. mentions in Integrated Ferroelectrics, Vol. 21, 273 (1998) that Pb(dpm)2-Zr(dpm)4-Ti(OiPr)2(dpm)2 will be the mainstream combination in future.
WO 98/51837 (November, 1998) discloses that, since thermal decomposition point of Zr(dpm)4 is considerably higher than that of Pb(dpm)2, the use of novel compounds which are Zr(OiPr)2(dpm)2 and Zr2(OiPr)6(dpm)2 instead of Zr(dpm)4 is preferred because they are apt to be decomposed at low temperature. The compounds claimed by the patent is Zrx(OR)yLz(in which R is an alkyl group; L is a xcex2-diketonate; x is 1 or 2; y is 2, 4 or 6; and z is 1 or 2). In the patent and also in an article by the inventor of the patent (Inorg. Chem., Vol. 38, 1432 (1999)), it is disclosed that Zr(OiPr)2(dpm)2 is a mixture and can be separated in Zr2(OiPr)6(dpm)2 and Zr(dpm)4 by a recrystallization.
Since Zr2(OiPr)6(dpm)2 is a dimer, its molecular weight is high and, according to a pamphlet (High Purity Precursors for Advanced Materials, p.15 (1999)) of Inorgtech, England, its sublimation temperature is 250xc2x0 C. at 0.1 Torr. It is true that the thermal decomposition temperatures of Zr(OiPr)2(dpm)2 and Zr2(OiPr)6(dpm)2 become lower but it is not preferred that the necessary sublimation temperature becomes high as compared with monomers.
Further, Zr(dpm)4 is soluble in THF at room temperature as good as 0.6 mol/liter but it is soluble in butyl acetate and in toluene to an extent of only about 0.2 mol/liter. Thus, there is a disadvantage that selection of the solvent is limited.
As a Zr compound for the formation of a PZT film using Pb(dpm)2, the invention provides a compound having a low reactivity with Pb(dpm)2, having a thermal decomposition temperature which is lower than Zr(dpm)4 and similar to Pb(dpm)2, showing a high sublimation pressure as a monomer and being well soluble in a solvent such as butyl acetate and toluene. The invention further provides a process for the manufacture of such a compound. The invention still further provides a liquid composition for the formation of a PZT film using the compound.
The Zr compound of the invention is a compound represented by the formula
Zr(OR)(L)3xe2x80x83xe2x80x83(formula I)
(in which R is an alkyl group having 1-5 carbon(s); and L is a xcex2-diketonate group).
The Zr compound of the invention is zirconium isopropoxy tris(dipivaloylmethanate) Zr(OiPr)(dpm)3 which is a compound of the formula I where R is isopropyl and L is dipivaloylmethanate.
A process for the manufacture of the Zr compound of the invention is a process where 1 mol of zirconium tetraalkoxide and 3 mol of a xcex2-diketone are made to react in an organic solvent, the solvent is evaporated therefrom and the residue is purified by sublimation in vacuo.
A process for the manufacture of zirconium isopropoxy tris(dipivaloylmethanate) Zr(OiPr)(dpm)3 of the invention is a process where 1 mol of zirconium tetraisopropoxide Zr(OiPr)4 and 3 mol of dipivaloylmethane dpmH are made to react in an organic solvent, the solvent is evaporated therefrom and the residue is purified by sublimation in vacuo.
The liquid composition for the formation of a PZT film according to the invention is a composition where the zirconium compound of the invention, lead bis(xcex2-diketonate) and titanium di(alkoxy)bis(xcex2-diketonate) are dissolved in an organic solvent.
The liquid composition for the formation of a PZT film according to the invention is a composition where zirconium isopropoxy tris(dipivaloylmethanate) Zr(OiPr)(dpm)3, lead bis(dipivaloylmethanate) Pb(dpm)2 and titanium di(isopropoxy)bis(dipivaloylmethanate) Ti(OiPr)2(dpm)2 are dissolved in an organic solvent.
The organic solvent in the liquid composition for the formation of a PZT film according to the invention is one solvent selected from a group consisting of butyl acetate, n-butyl ether, toluene and THF.